Opening labels having a forgery prevention function that can show signs of an item having been opened are well known. For example, transferring type seals are disclosed in Patent Publication 1, and non-transferring type seals are disclosed in Patent Publication 2. In addition, a technique that can prevent the reuse of opening seals is disclosed in Patent Publication 3.
Patent Publication 1 is Japanese Unexamined Patent Application Publication No. Hei 9-277423. Patent Publication 2 is Japanese Unexamined Patent Application Publication No. 2003-846672. Patent Publication 3 is Japanese Patent Publication No. 4565541.